Method and Apparatus for Evaluating the Potential Effectiveness of Refracing a Well

ABSTRACT

A method for evaluating the potential effectiveness of refracing a previously fracked oil/gas well is accomplished by isolating a plurality of previously fracked zones of an oil/gas well in a formation and measuring the fluid flow rates from the isolated zones using a three phase flow meter positioned within the well at or near the previously fracked zones. The zones may be isolated by an isolation assembly which includes two packers connected by a perforated pipe and attached to a tubular positioned within the well.

This application is a continuation of U.S. application Ser. No.14/829,602 filed Aug. 18, 2015 the entire contents of which is herebyincorporated herein by reference thereto.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to a method and apparatus for evaluating thepotential effectiveness of refracing an oil/gas well. Individualproduction zones are tested for flow rates of gas, water and oil todetermine which previously fracked production zones are the mostproductive and consequently the best candidates for refracing.

Description of Related Arts Invention

Currently when refracing a well the overall productivity of the well isconsidered before a decision to refrac is made. Little is known aboutwhich of the many perforated zones are productive in a well. Therefore,a method of determining which of the zones could benefit fromrefracturing is very important.

Furthermore, while some efforts have been made to measure the totalproduction of fluids within a well, very little effort has been made tomonitor the individual production rates for gas, water, and oil as wellas pressure and temperature at various stages of frac zones for thepurpose of evaluating the effectiveness of refracing an individual zoneusing the proposed method and tool configuration in this application.

Consequently there is a need to for a more precise method of measuringthe oil output of individual frac zones in order to evaluate thepotential effectiveness of refracing a given production zone.

BRIEF SUMMARY OF SOME OF THE PREFERRED EMBODIMENTS

These and other needs in the art are addressed in one embodiment byisolating individual frac zones of a previously fraced formation andmeasuring the Static Bottom Hole Pressure and Flowing Bottom HolePressure, so a productivity index can be calculated and the ratio ofOil, Gas and Water can be measured through the use of a three phase flowmeter, such as a Doppler flow meter. The production index is a measureof well's potential or ability to produce fluids as a function ofreduction in pressure. The production index (PI) is calculated bysubtracting the flowing bottom hole pressure (PF) from the static bottomhole pressure (PS) to get a drawdown pressure. The production rate inbarrels per day (bpd) is divided by the drawdown to arrive at the PI.Thus if the drawdown pressure is 500 psi and the producing rate is 500bpd, then the PI is 1.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter that form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand the specific embodiments disclosed may be readily utilized as abasis for modifying or designing other embodiments for carrying out thesame purposes of the present invention. It should also be realized bythose skilled in the art that such equivalent embodiments do not departfrom the spirit and scope of the invention as set forth in the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of the preferred embodiments of theinvention, reference will now be made to the accompanying drawing inwhich:

The FIGURE illustrates a schematic showing of a horizontal well having aplurality of frac zones with an embodiment of equipment for carrying outthe invention placed within the well.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The FIGURE shows a well 10 within formation 11 including a casing havinga horizontal portion 41 and a vertical portion 40 and a tubular string12 which may be coiled tubing or jointed pipe tubing.

As shown the well includes a vertical section and a horizontal portionwhich terminates at 42. However it is understood that the well mayconsist of a vertical section only surrounded by a plurality ofvertically spaced frac zones.

In a typical horizontally fraced well, there are a plurality of frackedzones 30, 31, 32, 33, 34, 35 wherein the casing 41 has been perforatedat 14, 15, 16, 17, 18, and 19. As is known in the art, fracing fluidsare introduced sequentially into the formation through the perforationsin the casing to fracture the formation adjacent the casing tofacilitate the flow of oil and other fluids from the formation to theinterior of the well.

According to an embodiment of the invention, coiled or jointed pipetubing 12 is lowered into the well and includes a jet pump section 20and, a pup joint 27 having a three phase flow meter 21 located withinthe pup joint.

An isolation assembly which includes a first packer 26, a perforated sub25, and a second packer 28 is attached to the tubing 12 at an endthereof via meter 27 and jet pump 21. When positioned within the well asshown in the FIGURE the isolation assembly will permit only fluid frompreviously fracked zone 34 to enter the interior of flow meter 21 viathe openings in perforated sub 25. When inflatable packers are used,power fluid from the jet pump may be diverted to the packers via aconduit 61 for inflating the packers.

To measure the flow rate of fluids from zone 34, power fluid isdelivered to jet pump 20 which will draw fluid from zone 34 throughperforated sub 25, packer 26 and pup joint 27. Consequently the threephase flow meter 21 in pup joint 27 will record the oil, gas and waterflow rates from the previously fraced zone 34. Flow meter 21 alsoincludes temperature and pressure gauges.

According to an embodiment of the invention, once the flow rate of afluid in a given frac zone has been measured, the flow rates of fluid inan different normally adjacent zone can be measured by moving theisolation unit to isolate a different frac zone such as frac zone 33shown in the FIGURE.

The Initial Bottom Hole Pressure will be measured before each zone istested and the straddle packers isolate that zone. The Flowing BottomHole Pressure will be measured when the jet pump is engaged and drawdownis achieved. Consequently the production index for each frac zone in aproducing well can be calculated. Based upon the calculation adetermination can be made as to the original frac zones that are mostlikely to exhibit increased productivity due to a refracing procedure.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations may be made herein without departing from the spirit andscope of the invention as defined by the appended claims.

What is claimed is:
 1. A method of evaluating the potentialeffectiveness of refracing a producing oil/gas well that has alreadybeen fracked at a plurality of zones along the length of the wellcomprising: a) isolating a first producing, previously fracked zone inthe well, b) measuring the oil, water, or gas flow rate, from theproducing zone while the zone is being produced, c) calculating aproduction index for the isolated previously fracked zone, and d)determining the previously fracked zones that are most likely to exhibitincreased productivity due to a refracing procedure based upon theproduction index.
 2. The method of claim 1 further including the step ofisolating two or more previously fracked zones and measuring the oilflow rate flow from each previously fracked zone.
 3. The method of claim1 wherein the previously fracked zone is isolated by placing a packerwithin the well at the beginning and end of the zone.
 4. The method ofclaim 3 wherein the oil, water, or gas flow rate is obtained by placinga three phase flow meter in tubing located within the well, the tubingincluding a perforated pipe positioned between the packers.
 5. Themethod of claim 4 wherein the oil, water, or gas is produced using a jetpump positioned within the production tubing.
 6. The method of claim 5wherein the packers are either of the inflatable type or mechanical typeand a portion of power fluid for the jet pump is diverted to set thepackers.
 7. The method of claim 1 wherein the well is a horizontal well.8. The method of claim 1 further including measuring the temperature andpressure of fluid within the previously fraced zone.
 9. The method ofclaim 1 further including measuring an initial static bottom holepressure and a flowing bottom hole pressure of the previously fracedzone, measuring a production rate of the previously fraced zone, whereinthe production index is calculated by subtracting the flowing bottomhole pressure from the static bottom hoe pressure and dividing theproduction rate by the result of subtracting the flowing bottom holepressure from the static bottom hole pressure.
 10. The method of claim 1further including the step of refracing the previously fraced zones thatare determined to be most likely to exhibit increased productivity.